Inferring cost of transport from whole-body kinematics in three sympatric turtle species with different locomotor habits.

Chelonians are mechanically unusual vertebrates as an exoskeleton limits their body wall mobility. They generally move slowly on land and have aquatic or semi-aquatic lifestyles. Somewhat surprisingly, the limited experimental work that has been done suggests that their energetic cost of transport (CoT) are relatively low. This study examines the mechanical evidence for CoT in three turtle species that have differing degrees of terrestrial activity. Our results show that Apolone travels faster than the other two species, and that Chelydra has higher levels of yaw. All the species show poor mean levels of energy recovery, and, whilst there is considerable variation, never show the high levels of energy recovery seen in cursorial quadrupeds. The mean mechanical CoT is 2 to 4 times higher than is generally seen in terrestrial animals. We therefore find no mechanical support for a low CoT in these species. This study illustrates the need for research on a wider range of chelonians to discover whether there are indeed general trends in mechanical and metabolic energy costs.